The authors point out in acronym-heavy style that comparing the environmental costs of electric vehicles (EVs) with internal combustion engine vehicles (ICEVs), it's important to do a life cycle assessment (LCA) that considers all aspects of producing the car, using the car, and the energy sources that propel the car, so as to take account of global warming potential (GWP) and other environmental costs. To make this more concrete, the comparison is between a car similar to a Nissan Leaf electric vehicle with a car similar to a conventional engine Mercedes A-series, which are comparable cars in size and power. Under certain conditions, electric cars are more environmentally friendly than conventional engines, but that conclusion holds only under certain conditions.

Source of electricity. If the electricity for the electric car is generated by wind power or hydroelectic power, then no carbon is emitted in producing that electricity. But if the electricity is generated by burning coal, carbon and a number of other pollutants are created. While electric cars reduce tailpipe emissions, it may be with a tradeoff of increasing emissions elsewhere. In addition, if the internal combustion engine is a diesel, it will run relatively clean. Thus, they write:

"When powered by average European electricity, EVs [electric vehicles) are found to reduce GWP [global warming potential] by 20% to 24% compared to gasoline ICEVs [internal combustion engine vehicles] and by 10% to 14% relative to diesel ICEVs under the base case assumption of a 150,000 km vehicle lifetime. When powered by electricity from natural gas, we estimate LiNCM [lithium-ion battery] EVs offer a reduction in GHG [greenhouse gas] emissions of 12% compared to gasoline ICEVs, and break even with diesel ICEVs. EVs powered by coal electricity are expected to cause an increase in GWP of 17% to 27% compared with diesel and gasoline ICEVs."

Number of miles the car is driven. Producing the large and powerful batteries needed for electric cars has environmental costs. By the calculations of this group, in a conventional car about 10% of the effect on climate change happens in production, and the rest in the use of the car over its lifetime. But for an electric car, about 50% of the effect on climate change happens in production, with the rest occurring over its lifetime (depending on the underlying source of the electricity used). As a result, the number of miles that a car is driven over its lifetime ends up making a big difference in its environmental effect. They write:

"Because production impacts are more significant for EVs than conventional vehicles, assuming a vehicle lifetime of 200,000 km exaggerates the GWP benefits of EVs to 27% to 29% relative to gasoline vehicles or 17% to 20% relative to diesel because production-related impacts are distributed across the longer lifetime. An assumption of 100,000 km decreases the benefit of EVs to 9% to 14% with respect to gasoline vehicles and results in impacts indistinguishable from those of a diesel vehicle."

The discussion ranges over a number of other factors: different technologies for making the batteries for electric cars, environmental costs of producing batteries, environmental costs of different sources for producing electricity, how often the batteries need to be replaced, environmental costs at the end of vehicle life, the efficiency of the vehicle in using energy, and other issues. They also note that electric vehicles are a technology that is developing and evolving quite rapidly, and so any calculation of costs and benefits will need to be updated. But as for where we stand right now, here's a summary:

"Our results clearly indicate that it is counterproductive to promote EVs in areas where electricity is primarily produced from lignite, coal, or even heavy oil combustion. At best, with such electricity mixes, local pollution reductions may be achieved. Thus EVs are a means of moving emissions away from the road rather than reducing them globally. Only limited benefits are achieved by EVs using electricity from natural gas. In the absence of foreseeable improvements to electricity mixes, a more significant reduction in GWP could potentially be achieved by increasing fuel efficiency or shifting from gasoline to diesel ICEVs without significant problem-shifting (with the exception of smog). ... Our results point to some probable problem shifts, irrespective of the electricity mix. EVs appear to cause a higher potential for human toxicity, freshwater eco-toxicity, freshwater eutrophication, and metal depletion impacts.... The many potential advantages of EVs should therefore serve as a motivation for cleaning up regional electricity mixes, but their promotion should not precede commitment to grid improvement."

But here's a coda from their analysis that struck me as interesting. Say for the sake of argument that a main effect of moving to electric cars was just to shift pollution to the factories that make batteries and to the facilities for generating electricity. It may be easier for society to set up incentives and programs for reducing pollution at a relatively few fixed big sites, rather than dealing with pollution from millions of tailpipes.

For some other recent examples of choices and tradeoffs that I've discussed on this blog, see: